1. Field of the Invention
The present invention relates to an electro-optical device typified by an EL (electroluminescence) display device formed by fabricating semiconductor elements (elements using a semiconductor thin film) on a surface of a substrate, and an electronic device including the electro-optical device as a display. Particularly, the invention relates to a method of manufacturing the same.
2. Description of the Related Art
In recent years, a technique for forming a thin film transistor (hereinafter referred to as a xe2x80x9cTFTxe2x80x9d) on a substrate has made remarkable progress, and its application and development to an active matrix type display device has proceeded. Especially, since a TFT using a semiconductor film that has a crystal structure (e.g., a polysilicon film) has a field effect mobility higher than a conventional TFT using an amorphous silicon film, a high speed operation can be made. Thus, it becomes possible to form a driving circuit that is connected to a pixel portion from the TFT, and to form the driving circuit on the same substrate.
Attention has been paid to such an active matrix type display device since various merits, such as reduction of manufacturing cost, miniaturization and thinning of a display device, increase of yield, and increase of throughput, can be obtained by forming various circuits and elements on the same substrate.
In the active matrix type EL display device, a switching element made of a TFT is provided for each pixel, and a driving element for making current control is operated by the switching element, so that an EL layer (light emitting layer) is made to emit light. For example, there is an EL display device disclosed in U.S. Pat. No. 5,684,365 (see Japanese Patent Application Laid-open No. Hei 8-234683), or Japanese Patent Application Laid-open Publication No. Hei 10-189252.
In methods of color display by these EL display devices, there have been trials of arranging EL layers which emit light of the three primary colors red (R), green (G), and blue (B) in each pixel. However, nearly all of the materials generally used as EL layers are organic materials, and it is difficult to apply a photolithography technique used in micro-machining as is. The reason is that the EL materials themselves are extremely weak with respect to moisture, and their handling is difficult in that they will easily dissolve in even a developer solution.
A technique of forming the EL layers by an ink-jet method has been proposed as a technique of solving these types of problems. For example, in Japanese Patent Application Laid-open No. Hei 10-012377 an active matrix type EL display in which the EL layer is formed by the ink-jet method is disclosed. Further, a similar technique is also disclosed in Shimada, T., et al., xe2x80x9cMulticolor Pixel Patterning of Light-Emitting, Polymers by Ink-jet Printing,xe2x80x9d SID 99 DIGEST, pp. 376-379.
It becomes possible to form an EL layer for each single pixel with the ink-jet method, and a process of patterning after forming the EL layer can be omitted. However, for both an active matrix type EL display device and for a passive type EL display device, as the screen size becomes larger and the pixel density increases, requirements for high positional precision and high speed processing increase.
The present invention aims to simplify the formation of an EL layer by an ink-jet method, and to perform high speed processing. An object of the present invention is to provide a method of manufacturing a high operation performance, high reliability electro-optical device, in particular a method of manufacturing an EL display device. In addition, an object of the present invention is to increase the quality of an electronic device having the EL display device as a display by increasing the picture quality of the electro-optical device.
In order to achieve the above objects, an EL layer is formed so as to be continuous over a plurality of pixels when the EL layer is formed by the ink-jet method. Specifically, the EL layers are formed continuously in a stripe pattern corresponding to a certain selected row or a column of pixel electrodes arranged in an m-column by n-row matrix state. Alternatively, an oblong shape or a rectangular shape EL layer is formed for each pixel electrode.
A predetermined pattern is formed with the ink jet method by repeatedly performing positional control of an ink head and discharge of ink (when an EL layer is formed, a liquid containing the EL layer material). Note that if the screen size becomes large or the pixel density becomes high, then the amount of processing time by this method for forming the EL layers corresponding to each pixel electrode becomes enormous. However, with the above method of forming the stripe stare or the oblong or rectangular shapes, it becomes possible to form the EL layers by continuously scanning the ink head and the amount of processing time can be shortened.
In manufacturing a color display EL display device, EL layers corresponding to each or the colors red, green, and blue may be formed so as to form stripes, or in an oblong shape or a rectangular shape. This type of EL layer and EL layer manufacturing method can be applied to an active matrix type display and to a passive matrix type display.
In addition, the diffusion of alkali metals from EL elements formed by the ink-jet method is prevented by an insulating film (passivation film) formed between the EL elements and TFTs with the present invention. Specifically, an insulating film for preventing transmission of alkali metals is formed is on a leveling film covering the TFTs. In other words, a material may be used in which the diffusion speed of alkali metals throughout the insulating film at the operation temperature of the EL display device is sufficiently low.
Preferably, an insulating film through which moisture and alkali metals are not transmitted and having a high thermal conductivity (high heat radiating effect) is selected, and the insulating film is formed contacting the EL elements, or more preferably that type of insulating film has a state in which it surrounds the EL elements. Namely, the insulating film having a blocking effect against moisture and alkali metals, and having a heat radiating effect, is formed in a location as close as possible to the EL elements, and deterioration of the EL elements is suppressed by the insulating film.
Further, when a single layer cannot be used as that type of insulating film, an insulating film having a blocking effect against moisture and alkali metals, and an insulating film having a heat radiating effect can be laminated and used. In addition, an insulating film having a blocking effect against moisture, an insulating film having a blocking effect against alkali metals, and an insulating film having a heat radiating effect can also be laminated and used.